Medico - Surgical Devices

ABSTRACT

An embryo replacement catheter has a flexible extruded shaft of a transparent polyurethane with a bore extending along its length. Gas bubbles of a diameter in the range 5μ to 10μ are incorporated into the thickness of the wall of the shaft by adding gas during extrusion. The bubbles are selected to increase the visibility of the catheter under ultrasound imaging whilst still enabling material flowing along the catheter to be seen.

BACKGROUND OF THE INVENTION

This invention relates to medico-surgical devices.

The invention is more particularly concerned with medico-surgicaldevices, such as catheters, that are visible under ultrasoundobservation.

Ultrasound imaging equipment is increasingly being used during surgicalprocedures to monitor the location of a device within the body. Thevisibility of a device under ultrasound depends on various factorsincluding the difference between the acoustic impedance of the materialof the device and that of the surrounding medium, such as the patienttissue or body fluid within which the device is located. This differenceis relatively low with plastic devices such as catheters and may makeconventional catheters difficult to locate. Even devices of metal, suchas needles, present problems of visibility under ultrasound observationbecause of the directional nature of the reflections. In someorientations a metal needle may be clearly visible but in otherorientations it may be considerably less visible.

Attempts have been made to increase the visibility of medico-surgicaldevices under ultrasound observation in various ways. The surface of thedevice may be modified, such as by forming grooves or indentations inits surface. A reflective coating may be applied to the device, such asincorporating bubbles, as described in WO98/19713 and EP0624342.

Alternatively, a metal marker may be secured to a plastics catheter.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide an alternativemedico-surgical device.

According to one aspect of the present invention there is provided amedico-surgical device of a plastics material, the material includinggas bubbles through the major part of the thickness of the material inat least a part of the device such as to increase the visibility of thedevice under ultrasound imaging.

The device is preferably tubular and the gas bubbles may be providedaround the entire circumference of the device or may be provided in aregion of the device occupying only a part of the circumference of thedevice, such as a strip extending along the length of the device. Theouter surface of the device may be smooth and uninterrupted by gasbubbles, and the device may have an inner surface that is smooth anduninterrupted by gas bubbles. The bubbles may have a diameter in therange 1μ to 50μ and preferably have a diameter in the range 5μ to 10μ.The bubbles may be substantially spherical. The device may be extruded,the gas bubbles being formed by addition of gas during extrusion of thedevice. Alternatively, the gas bubbles may be formed by a chemicalfoaming agent or by the incorporation of hollow microspheres into theplastics material. The plastics material is preferably substantiallytransparent, the size and density of the bubbles being selected such asto enable material flowing along the device to be viewed by the eye. Theplastics material may be polyurethane.

According to another aspect of the present invention there is providedan embryo replacement catheter comprising a flexible, hollow, extrudedshaft of a substantially transparent plastics material, the shaftincluding gas bubbles through the thickness of its wall, the density andsize of the bubbles being selected to increase visibility of thecatheter under ultrasound imaging whilst enabling an embryo within thecatheter to be viewed by the eye, and the bore of the catheter beingsmooth and uninterrupted by the gas bubbles.

According to a further aspect of the present invention there is provideda method of making a medico-surgical device comprising the steps ofextruding a plastics material while incorporating a gas into the wall ofthe device such as to form gas bubbles through the major part of thethickness of the wall of the device sufficient to increase thevisibility of the device under ultrasound observation.

According to a fourth aspect of the present invention there is provideda method of making a medico-surgical device comprising forming a wall ofa plastics material containing a chemical foaming agent such as to formgas bubbles through the major part of the thickness of the wall of thedevice sufficient to increase the visibility of the device underultrasound observation.

According to a fifth aspect of the present invention there is provided amethod of making a medico-surgical device comprising forming a wall of aplastics material containing hollow microspheres such as to form gasbubbles through the major part of the thickness of the wall of thedevice sufficient to increase the visibility of the device underultrasound observation.

According to a sixth aspect of the present invention there is provided adevice made by a method according to the above further aspect of thepresent invention.

An embryo-transfer catheter and its method of manufacture; according tothe present invention, will now be described, by way of example, withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side elevation view of the catheter;

FIG. 2 is a sectional side elevation view of a part of the catheter ofFIG. 1 to a larger scale;

FIG. 3 illustrates schematically manufacture of the catheter; and

FIG. 4 is a sectional transverse view through an alternative catheter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference first to FIGS. 1 and 2, the catheter comprises a flexibleshaft 1 and a hub 2 joined at the rear end of the shaft. The shaft 1 hasa circular section and a bore 10 extending along its length. The shaft 1opens at its forward, right-hand, patient end 11, which isatraumatically rounded. The shaft 1 is extruded from a clear,transparent polyurethane material and incorporates small, gas-filledbubbles 12 the size and distribution of which are selected to increasethe visibility of the catheter under ultrasound observation. Typically,the gas bubbles have a diameter in the range of about 0.1 to 300,preferably being between 1μ and 50μ with the most preferred range being5μ to 10μ. The bubbles 12 extend through the entire thickness of thewall of the shaft 1 and may be spherical or of any other regular orirregular shape. The outer and inner surfaces 13 and 14 of the shaft maybe smooth and uninterrupted by gas bubbles or the bubbles may break thesurface.

The hub 2 serves to make connection with the shaft 1 and is moulded froma rigid, transparent plastics material, being subsequently bonded withthe rear end of the shaft.

The shaft 1 is extruded in the manner shown in FIG. 3 using an extrusionmachine 20. Polyurethane material 21 is heated and supplied to theextrusion head 22 in the usual way but a gas such as nitrogen of carbondioxide is also injected through the inlet 23 under pressure into themelt. As the plastics emerges from the extrusion head 22 the gas expandsto form the bubbles 12. The relatively gas-permeable nature of theplastics means that after manufacture the bubble-forming gas willquickly escape and be replaced with air.

The shaft 1 can be extruded continuously at low cost, without the needfor any subsequent operations apart from attaching the hub 2 and endforming the patient end tip 11.

The catheter shaft could be formed by other melt processes, such asinjection moulding or blow moulding.

The bubbles could be formed in ways other than by injection of gas intothe melt. For example, chemical foaming agents could be added to theplastics material, such as: azocarbonomides,dinitrosopentmethelyene-tetramine, benzenephonohydrazine, 4,4oxybis(benzenephonohydrazine), NN¹dimethyl-NN¹ dinitrosoterephthalamide,azoisobutyronitrile, sodium bicarbonate, terephthalazide ortrihydrazinatrazine. Another way of forming the gas bubbles would be byincorporating a liquid into the plastics melt which volatises during themelt process. Alternatively, solid powdered dry ice (carbon dioxide)could be incorporated into the melt so that the particles of dry icebecome gas bubbles during the forming process. It might be possible touse other solids which undergo sublimation in this way. The bubblescould be formed directly as a result of chemical reaction duringpolymerisation and or alternatively during cross-linking. The bubblescould be formed mechanically by whipping the plastics in a liquid form,such as in the manner used to form latex foam. The bubbles could beformed by the incorporation of hollow microspheres of resin or glass.Alternatively, small particles of a soluble material could be added tothe plastics melt and subsequently dissolved away.

A shaft of this kind can have good visibility under ultrasound imagingwithout producing multiple echoes and can produce a good imageregardless of the orientation of the shaft. The shaft can be madesufficiently transparent to ultrasound energy to enable material flowingalong the bore of the catheter to be observed on the ultrasound image.

Because the catheter does not require any coating or separate markerthere is no need for subsequent assembly operations and there is no riskof detachment. The catheter can be made of conventionalmedically-approved materials so does not present any new risk to thepatient. Because the surface of the catheter can be smooth, the cathetercan be inserted or slid through an outer tube with low friction. Thesmooth bore of the catheter ensures free flow along the bore, which canbe important where the catheter is used to transfer embryos. The smoothsurfaces also reduce the accumulation of biofilm on the catheter. Thecatheter can be made without the need for metal components, which can bean advantage where the catheter is used while the patient is beingviewed by magnetic imaging techniques. The catheter can be completelytransparent to x-rays or the plastics from which it is formed couldincorporate an x-ray opaque filler, such as barium sulphate.

The bubble size and density can be selected so that the opticaltransparency of the plastics forming the shaft remains sufficient toenable material flowing along the shaft to be viewed by the eye.

There are various ways in which the catheter could be modified. Forexample, it could be preferable for the bubbles to have a non-sphericalshape and be oriented in a particular direction, such as longitudinally.This could be achieved by means of an obstruction in the extrusion diethat constricts and elongates the bubbles as they flow through. Such anarrangement may give an increase in ultrasound visibility whilstreducing the opacity of the shaft to the eye.

It is not essential for the bubbles to be provided around the entirecircumference of the shaft. As shown in FIG. 4, the bubbles 12′ could beformed only in one or more stripes extending along the shaft 1′, such asin the stripe 40. This arrangement can be used where the shaft needs tohave increased clarity so that material within the catheter can be seenby the eye. The bubble region need not be continuous along the length ofthe catheter. Instead, discrete separate regions with bubbles could beseparated from one another along the length of the catheter by regionswithout bubbles. A shaft for such a catheter could be made byinterrupting gas flow to the extruder. Where the bubbles are containedwithin a stripe, this could be interrupted to make it discontinuous byextruding the stripe using two auxiliary extruders, one having materialwith a blowing agent and the other having material without the blowingagent. Alternate extruders are switched on and off so that the stripecan have sections containing bubbles separated from one another bysections without bubbles. A catheter with an interrupted bubble regionmay give a clearer ultrasound indication of movement of the catheteralong its length and may also enable clearer observation of materialflowing along the catheter both by ultrasound and by the eye.

1-18. (canceled)
 19. An embryo replacement catheter comprising: a hub;and a shaft attached to the hub, the shaft having a bore extendingtherethrough, the shaft comprising a wall of a transparent plasticmaterial with gas bubbles incorporated therein, wherein the gas bubblesextend through a major part of a thickness of the wall of the shaft, andthe gas bubbles have a density and size to enable visibility of thecatheter under ultrasound imaging and to enable an embryo within thebore of the shaft to be viewed by a naked eye of the user.
 20. Theembryo replacement catheter of claim 19, wherein an outer surface of thewall of the shaft forms an outer surface of the catheter.
 21. The embryoreplacement catheter of claim 20, wherein the shaft has an inner surfacethat is smooth and uninterrupted by the gas bubbles.
 22. The embryoreplacement catheter of claim 19, wherein the bore is smooth anduninterrupted by the gas bubbles.
 23. The embryo replacement catheter ofclaim 19, wherein the shaft is tubular.
 24. The embryo replacementcatheter of claim 19, wherein the shaft is flexible.
 25. The embryoreplacement catheter of claim 19, wherein the gas bubbles extend aroundan entire circumference of the shaft.
 26. The embryo replacementcatheter of claim 19, wherein the gas bubbles extend around a firstportion of a circumference of the shaft, a second portion of thecircumference of the shaft being free of the gas bubbles.
 27. The embryoreplacement catheter of claim 19, wherein the shaft has an outer surfacethat is smooth and uninterrupted by the gas bubbles.
 28. The embryoreplacement catheter of claim 19, wherein the shaft has an inner surfacethat is smooth and uninterrupted by the gas bubbles.
 29. The embryoreplacement catheter of claim 19, wherein the gas bubbles have a nominaldiameter of 1μ to 50μ.
 30. The embryo replacement catheter of claim 19,wherein the gas bubbles have a nominal diameter of 5μ to 10μ.
 31. Theembryo replacement catheter of claim 19, wherein the gas bubbles aresubstantially spherical.
 32. The embryo replacement catheter of claim19, wherein the shaft is extruded, and the gas bubbles are formed byintroducing gas to the plastic material, in a molten state, duringextrusion of the shaft.
 33. The embryo replacement catheter of claim 19,wherein the plastic material is polyurethane.
 34. The embryo replacementcatheter of claim 19, wherein the hub is formed of a transparentmaterial.
 35. The embryo replacement catheter of claim 34, wherein thetransparent material is a plastic.